This invention is related to a method of making the heat resistant polyester which has reduced amount of end carboxyl groups.
In order to improve the heat stability of polyester, i.e., the resistance to hydrolysis and to aminolysis at high temperature, reduction of the amount of end carboxyl groups (hereinafter this will be written as (COOH)) is well known to be an effective method. Many methods of reducing the (COOH) of polyester have been proposed. Among them, the method of reacting the polyester with an epoxy compound is known as a typical example. Study of this method shows that, by the addition of an epoxy compound, the (COOH) decreases, but there arise the problems such as the reduction in degree of polymerization and the insufficient reactivity of (COOH) in some epoxy compounds with which the effect is not sufficient.